The present invention relates to a process for producing vinylaromatic polymers having a high degree of syndiotacticity. More particularly, the present invention relates to such a process that is capable of forming such polymers in an efficient manner using hydrogen gas to improve catalyst efficiency.
It is previously known in the art to prepare vinylaromatic polymers having a high degree of syndiotacticity. In U.S. Pat. Nos. 5,037,907 and 5,254,647 suitable reactor designs, catalysts and processing conditions are taught.
In U.S. Pat. No. 4,990,580, the use of hydrogen at a partial pressure within the range of 0.01 to 50 kg/cm.sup.2 (1 to 5000 kPa) in order to control the molecular weight of the resulting syndiotactic vinylaromatic polymer product was taught. The reference did not indicate any benefit in catalyst efficiency in the use of hydrogen pressures within any particular range. The examples did not utilize extremely small hydrogen pressures and the reference did not indicate any importance in maintaining a relatively constant but low hydrogen pressure throughout the polymerization.
For the teachings contained therein, the foregoing U.S. patents are herein incorporated by reference.